Although lead has been traditionally used in numerous industrial applications, current regulations have mandated the phase out of lead in most commercial products. For example, the European Union issued regulations in 2006 that mandated the elimination of lead from coatings and solders used in most electronic components. Other countries have issued similar mandates.
Soldering applications, particularly in electronics and vehicle manufacturing, have been heavily impacted by the ban on lead. Although many alternatives to traditional lead-based solders have been developed, the Sn/Ag/Cu (SAC) system being among the most widely used, such replacements have typically exhibited drawbacks that make them unsuitable for extreme environments such as those found in automotive, military and space vehicles, for example. Specifically, the SAC system has a significantly higher eutectic melting point (e.g., m.p. of ˜217° C.) than does traditional Sn/Pb solder (m.p. of 183° C. for 63/37 Sn/Pb or 188° C. for 60/40 Sn/Pb), thus limiting its use to materials that are capable of withstanding its higher processing temperature. Further, silver is a relatively expensive component in the SAC system. From an economic standpoint, the SAC system can undesirably lead to significantly higher production costs due to the material cost of silver and the more robust components needed to withstand its higher processing temperature. Even more importantly, current SAC systems are prone to formation of tin whiskers on the solder joint over its lifetime, thereby increasing the risk of electrical shorting.
Several compositions containing nanoparticles have also been proposed as replacements for traditional lead-based solders. Nanoparticles can exhibit physical and chemical properties that sometimes differ significantly from those observed in the bulk material. For example, copper nanoparticles having sizes of less than about 20 nm can exhibit a fusion temperature that is significantly below the melting point of bulk copper. Thus, a copper nanoparticle system has been tested for use as a lead solder replacement. However, the copper nanoparticle system does not allow for easy rework when replacement of failed components becomes necessary.
In view of the foregoing, more suitable replacements for traditional lead-based solder materials are needed. The present invention satisfies this need and provides related advantages as well.